EP2791377B1 - Process for manufacturing a thin strip made of soft magnetic alloy - Google Patents

Description

The present invention relates to the manufacture of soft magnetic alloy strip of iron-cobalt type.

Many electrotechnical equipment includes magnetic parts and in particular magnetic yokes made of soft magnetic alloys. This is the case in particular of the electric generators embedded in vehicles in particular in the field of aeronautics, railway or automobile. Generally, the alloys used are alloys of the iron-cobalt type and in particular alloys comprising approximately 50% by weight of cobalt. These alloys have the advantage of having a very high saturation induction, a high permeability to working inductions equal to or greater than 1.6 Tesla and a fairly high resistivity allowing a reduction of AC and high induction losses. When in common use, these alloys have a strength corresponding to a yield strength of between about 300 and 500 MPa. However, for some applications, it is desirable to have high elastic limit alloys whose yield strength can reach or exceed 600 MPa, or even in some cases 900 MPa. The latter so-called HLE alloys are particularly useful for producing miniaturized alternators embedded on aircraft. These alternators are characterized by very high speeds of rotation exceeding 20,000 rpm which require a high mechanical resistance of the components constituting the magnetic yokes. In order to achieve the characteristics of high yield strength alloys, it has been proposed in various patents to add various alloying elements such as Niobium, Carbon and Boron in particular.

All these materials containing from 15 to 55% by weight of cobalt, whether they have an approximately equi-atomic Fe-Co composition, or that they contain much more iron than cobalt, must be subjected to an annealing adapted to obtain the desired use properties, and in particular a good compromise between the mechanical characteristics and the magnetic characteristics sought for the uses for which they are intended. For these alloys, it is known, well established, and practiced that the electrotechnical parts (stators, rotor and other various profiles) are cut in strips of hardened material obtained by cold rolling to the final thickness. After cutting, the parts are systematically subject, in the last step, to a static annealing to adjust the magnetic properties. Static annealing in the state of the art of Fe-Co alloys, a heat treatment during which the cut pieces are maintained above 200 ° C for at least 1 hour and are passed through a temperature greater than or equal to 700 ° C, at which a bearing is imposed. By step is meant a period of time of at least 10 minutes during which the temperature varies at most 20 ° C above or below a set temperature. In this treatment, the ascents and descents between the ambient and the bearing generally take a time of at least 1 hour in the industrial production regime. Therefore, an industrial "static" annealing treatment, allowing a good optimization of the magnetic performances, includes for this a temperature step of one to several hours: the "static" annealing thus takes several hours.

In a manner known in itself to those skilled in the art, the cold rolling is carried out on strips of thickness generally of the order of 2 to 2.5 mm, obtained by hot rolling and then subjected to a quenching. . This makes it possible to avoid, to a large extent, the order / disorder transformation in the material, which therefore remains almost disordered, but little changed with respect to its structural state at a temperature above 700 ° C. As a result of this treatment, the material can then be cold rolled unhindered to the final thickness.

The strips thus obtained then have sufficient ductility to be cut by mechanical cutting. Also, when they are intended to manufacture magnetic yokes consisting of stack of pieces cut in thin strips, these alloys are sold to users in the form of strips in the hardened state. The user then cuts the pieces, stacks them and assembles or assembles the magnetic yokes, and then carries out the thermal treatment of quality necessary to obtain the desired properties. This quality heat treatment aims to obtain a certain development of grain growth after recrystallization, because it is the grain size that sets the compromise between mechanical and magnetic performance. Depending on the parts considered of the electrotechnical machine, the performance compromises, and therefore the heat treatments, may be different. Thus, in general, aeronautical edge generator stators and rotors are cut together in the same strip portion to minimize metal scrap. But, the rotor undergoes a heat treatment favoring relatively high mechanical performance, typically a temperature below 800 ° C, while the stator is subjected to a heat treatment optimizing the magnetic performance (thus to higher average grain size) typically a higher temperature at 800 ° C.

In addition, this quality heat treatment may comprise for each type of cut piece, two anneals, one to adjust the magnetic and mechanical properties as we have just seen and the other to oxidize the surfaces of the sheets in order to reduce the inter-laminar magnetic losses. This second annealing may also be replaced by a deposit of an organic material, mineral or mixed.

• la nécessité de changer d'alliage (compliqué, stock plus importants, plus couteux) lorsqu'on souhaite atteindre des limites élastiques d'au moins 500 à 600MPa ; en effet l'alliage FeCo connu par l'homme du métier pour convenir à la plupart des applications électrotechniques, peut atteindre des propriétés magnétiques douces telles que un champ coercitif de 0,4 à 0,6 Oe (32 à 48 A/m) lorsque le recuit est réalisé à au moins 850°C et aussi peut atteindre une limite élastique de 450-500MPa lorsque la température de recuit est abaissée en dessous de 750°C ; dans tous les cas la limite élastique n'atteint jamais 600MPa sur le même alliage ; pour y parvenir d'autres alliages, légèrement différents en composition, utilisant notamment des précipités ou 2^nde phase, doivent être utilisés ;
• la nécessité pour l'utilisateur de recuire toutes les pièces découpées (que la nuance soit à haute limite élastique (HLE) ou non), en effet, après recuit statique, l'alliage est trop fragile pour pouvoir être découpé par des moyens mécaniques ;
• la nécessité de devoir supporter des pertes magnétiques élevées pour des limites élastiques d'au moins 500MPa ;
• la difficulté voire l'impossibilité pour des performances HLE d'atteindre par le traitement thermique, un compromis précis en performances mécaniques et magnétiques ; en effet, en théorie il est toujours possible d'obtenir des performances HLE (500 à 1200MPa de limite d'élasticité) par un « recuit statique » tel que défini ci-dessus en appliquant des paliers de température entre 700 et 720°C, donc dans un état métallurgique allant de l'état écroui puis restauré à un état plus ou moins cristallisé et propre à ce type de recuit ; mais en pratique, dans cette plage 500-1200MPa, la limite élastique dépend très sensiblement de la température de palier au degré près ; cette hypersensibilité des performances à la température de palier interdit la transposition industrielle puisque les fours industriels statiques ne peuvent en général pas assurer une homogénéité de température de la charge à recuire meilleure que + /-10 °C, soit l'étendue de la plage de réglage de la limite élastique entre 500 et 1200MPa ; exceptionnellement cette homogénéité peut être de +/-5°C ; cependant, cela n'est pas suffisant pour maîtriser une fabrication industrielle.
• la difficulté d'atteindre des cotes précises de pièce finie lorsque le recuit statique final s'applique à des pièces découpées dans le métal écroui, de géométrie complexe (exemple pièce/profil en E de transformateur à jambes allongées).

The disadvantages of the technique according to this prior art are numerous and mention may be made in particular of:

• the need to change the alloy (complicated, larger stock, more expensive) when it is desired to reach elastic limits of at least 500 to 600 MPa; indeed the FeCo alloy known to those skilled in the art to suit most electrotechnical applications, can achieve soft magnetic properties such as a coercive force of 0.4 to 0.6 Oe (32 to 48 A / m) when the annealing is performed at at least 850 ° C and also can reach a yield strength of 450-500MPa when the annealing temperature is lowered below 750 ° C; in all cases the elastic limit never reaches 600 MPa on the same alloy; to achieve other alloys, slightly different in composition, in particular using precipitates or 2 ^nd stage, must be used;
• the need for the user to anneal all the cut pieces (that the grade is high elastic limit (HLE) or not), in fact, after static annealing, the alloy is too fragile to be cut by mechanical means;
• the need to withstand high magnetic losses for elastic limits of at least 500 MPa;
• the difficulty or even the impossibility for HLE performances of achieving heat treatment, a precise compromise in mechanical and magnetic performance; indeed, in theory it is always possible to obtain HLE performances (500 to 1200 MPa of elastic limit) by a "static annealing" as defined above by applying temperature steps between 700 and 720 ° C. therefore in a metallurgical state ranging from the hardened state then restored to a more or less crystallized state and suitable for this type of annealing; but in practice, in this range 500-1200MPa, the elastic limit depends very substantially on the bearing temperature to the nearest degree; this hypersensitivity of performance at bearing temperature prohibits industrial transposition, since static industrial furnaces generally can not ensure a temperature homogeneity of the charge to be annealed better than + / -10 ° C, ie the range of the adjustment of the elastic limit between 500 and 1200 MPa; exceptionally this homogeneity can be +/- 5 ° C; however, this is not enough to control industrial manufacturing.
• the difficulty of reaching precise dimensions of the finished part when the final static annealing applies to parts cut in the hardened metal, of complex geometry (example piece / E profile of transformer with elongated legs).

It is also known from the document US 3,622,409 a method of manufacturing soft magnetic alloy iron-cobalt alloy parts, comprising continuous annealing.

The object of the present invention is to remedy these drawbacks by proposing a method for manufacturing a thin strip of soft magnetic alloy type iron-cobalt which, from the same alloy, allows to propose an easily cutable strip that can have as well , in a predefined manner, a yield strength that is both medium and very high while retaining the possibility of obtaining good to very good magnetic properties by subsequently applying a second static heat treatment or parade, the alloy being able to pass from a high yield state to a high magnetic performance state under the effect of an annealing such as, for example, a conventional static annealing, the alloy having, in addition, a good aging resistance of its mechanical properties up to 200 ° C.

To this end, the subject of the invention is a process for producing a band of a soft magnetic alloy capable of being mechanically cut, the chemical composition of which comprises, by weight: 18% ≤ Co ≤ 55% 0% ≤ V + W ≤ 3% 0% ≤ Cr ≤ 3% 0% ≤ Yes ≤ 3% 0% ≤ Nb ≤ 0.5% 0% ≤ B ≤ 0.05% 0% ≤ VS ≤ 0.1% 0% ≤ Zr + Ta ≤ 0.5% 0% ≤ Or ≤ 5% 0% ≤ mn ≤ 2% The rest being iron and impurities resulting from the elaboration,

According to this method, a strip obtained by hot rolling of a half product made of this alloy is cold rolled to obtain a cold-rolled strip of thickness typically less than 0.6 mm and, after cold rolling, performs on-band annealing treatment by passing through a continuous furnace, at a temperature between the order / disorder transition temperature of the alloy (for example 700-710 ° C. for Fe-49% Co-2% V alloy well known to those skilled in the art) and the ferritic / austenitic transformation start temperature of the alloy (typically 880 to 950 ° C. for the FeCo alloys of the invention), followed by rapid cooling to a temperature below 200 ° C.

The annealing temperature is preferably between 700 ° C and 930 ° C.

Preferably, the running speed of the strip is adapted so that the residence time of the strip at the annealing temperature is less than 10 minutes.

Preferably, the cooling rate of the strip at the outlet of the treatment furnace is greater than 1000 ° C./h.

According to the invention, the speed of travel of the strip in the furnace and the annealing temperature are adapted to adjust the mechanical strength of the strip.

Preferably, the chemical composition of the alloy is such that: 47% ≤ Co ≤ 49.5% 0.5% ≤ V ≤ 2.5% 0% ≤ Your ≤ 0.5% 0% ≤ Nb ≤ 0.5% 0% ≤ Cr < 0.1% 0% ≤ Yes < 0.1% 0% ≤ Or < 0.1% 0% ≤ mn < 0.1%

• soit du type « partiellement cristallisée », c'est-à-dire que, sur au moins 10% de la surface d'échantillons observés au microscope avec un grossissement de x 40 après attaque chimique au perchlorure de fer, il n'est pas possible d'identifier des joints de grain ;
• soit du type « cristallisée », c'est-à-dire que sur au moins 90% de la surface d'échantillons observés au microscope avec un grossissement de x 40 après attaque chimique au perchlorure de fer, il est possible d'identifier un réseau de joints de grains et, dans la plage des tailles de grain allant de 0 à 60 µm², il existe au moins une classe de 10 µm² de largeur de taille de grains comprenant au moins deux fois plus de grains que la même classe de taille de grains correspondant à l'observation d'une bande laminée à froid de comparaison ayant la même composition, n'ayant pas été soumise à un recuit continu mais ayant été soumise à un recuit statique à une température telle que l'écart entre champ coercitif obtenu avec le recuit statique et le champ coercitif obtenu avec le recuit au défilé est inférieur à la moitié de la valeur du champ coercitif obtenu par le traitement au défilé et, dans la plage de taille de grains allant de 0 à 60 µm², il existe au moins une taille de classe de grains de 10 µm² de largeur dont le rapport du nombre de grains au nombre total de grains observés sur l'échantillon ayant subi un recuit au défilé est supérieur d'au moins 50% au même rapport correspondant à un échantillon prélevé sur la bande laminée à froid de comparaison ayant subi un recuit statique.

This method has the advantage of making it possible to manufacture a thin strip which can be easily cut by mechanical means and which is distinguished from bands known by its metallurgical structure. In particular, the band obtained by this method is a cold-rolled soft magnetic alloy strip, less than 0.6 mm thick, made of an alloy whose chemical composition comprises, by weight: 18% ≤ Co ≤ 55% 0% ≤ V + W ≤ 3% 0% ≤ Cr ≤ 3% 0% ≤ Yes ≤ 3% 0% ≤ Nb ≤ 0.5% 0% ≤ B ≤ 0.05% 0% ≤ VS ≤ 0.1% 0% ≤ Zr + Ta ≤ 0.5% 0% ≤ Or ≤ 5% 0% ≤ mn ≤ 2% the rest being iron and impurities resulting from the elaboration, whose metallurgical structure is:

• either of the "partially crystallized" type, that is to say that, on at least 10% of the surface of samples observed under a microscope with a magnification of x 40 after chemical attack with iron perchloride, it is not possible to identify grain boundaries;
• either of the "crystallized" type, that is to say that on at least 90% of the surface of samples observed under a microscope with a magnification of x 40 after chemical attack with iron perchloride, it is possible to identify a grain boundary network and, in the range of grain sizes from 0 to 60 μm ² , there is at least one class of 10 μm ² of grain size width comprising at least twice as many grains as the same class of grain size corresponding to the observation of a comparative cold rolled strip having the same composition, not having been continuously annealed but having been subjected to static annealing at a temperature such that the difference between Coercive field obtained with static annealing and the coercive field obtained with run-on annealing is less than half of the value of the coercive field obtained by the run-on treatment and, in the grain size range from 0 to 60 μm ² , it exists at least a grain class size of 10 μm ² in width, the ratio of the number of grains to the total number of grains observed on the par-milled sample is at least 50% greater than the same ratio corresponding to a sample taken from the cold rolled comparative static annealed strip.

As is obvious to those skilled in the art, the term "crystallized" is used herein as synonymous with "recrystallized. Indeed, the cold-rolled strip in the form of a thin strip is totally hardened, that is to say that the crystalline order is totally dislocated at long distance, and that the notion of crystals or "grain" no longer exists. . The annealing treatment with the parade then makes it possible to "crystallize" this matrix worked in crystals or grains. This phenomenon is nevertheless also called recrystallization because it is not the first crystallization undergone by the alloy since its development phase from the solidified liquid metal.

Preferably, the chemical composition of the soft magnetic alloy is such that: 47% ≤ Co ≤ 49.5% 0.5% ≤ V ≤ 2.5% 0% ≤ Your ≤ 0.5% 0% ≤ Nb ≤ 0.5% 0% ≤ Cr ≤ 0.1% 0% ≤ Yes ≤ 0.1% 0% ≤ Or ≤ 0.1% 0% ≤ mn ≤ 0.1% and the elastic limit R _P0,2 is between 590 MPa and 1100 MPa, the coercive field Hc is between 120 A / m and 900 A / m, the magnetic induction B for a field of 1600 A / m is between 1.5 and 1.9 Tesla.

In addition, the saturation magnetization of the band is greater than 2.25 T.

With this strip it is possible to manufacture parts for magnetic components, for example rotor and stator parts, and in particular for magnetic yokes, and magnetic components such as magnetic yokes, by directly cutting the parts in a strip according to the invention. then, if necessary, by assembling the parts thus cut in such a way as to constitute components such as cylinder heads, and possibly causing some of them (for example the stator parts only) or to some of them ( for example stator yokes) a complementary annealing treatment to optimize the magnetic properties, and in particular to minimize magnetic losses.

Also, the invention also relates to a method for manufacturing a magnetic component according to which a plurality of parts is cut by mechanical cutting in a strip obtained by the preceding method, and, after cutting, the parts are assembled to form a magnetic component. .

In addition, the magnetic component or the parts can be subjected to a static annealing of quality, that is to say, an annealing of optimization of the magnetic properties.

Preferably, the static annealing of quality or of optimization of the magnetic properties is annealing at a temperature of between 820 ° C. and 880 ° C. for a time of between 1 hour and 5 hours.

The magnetic component is for example a magnetic yoke.

The invention will now be described in a more precise but nonlimiting manner and illustrated by examples.

In the manufacture of cold-rolled thin strips for mechanical cutting of magnetic yoke parts of electrotechnical equipment, an alloy known per se is used, the chemical composition of which comprises by weight: from 18% to 55% of cobalt, 0% to 3% Vanadium and / or Tungsten, 0% to 3% Chromium, 0% to 3% Silicon, 0% to 0.5% Niobium, 0% to 0.05% % boron, 0% to 0.1% C, 0% to 0.5% zirconium and / or tantalum, 0% to 5% nickel, 0% to 2% manganese, the rest being iron and impurities resulting from the elaboration.

Preferably, the alloy contains 47% to 49.5% Cobalt, 0% to 3% Vanadium plus Tungsten, 0% to 0.5% Tantalum, 0% to 0.5% of Nobium, less than 0.1% chromium, less than 0.1% silicon, less than 0.1% nickel, less than 0.1% manganese.

In addition, the vanadium content should preferably be greater than or equal to 0.5% in order to improve the magnetic properties and better escape the weakening ordering during rapid cooling, and remain less than or equal to 2, 5% in order to avoid the presence of the second non-magnetic austenitic phase, tungsten not being indispensable, and the niobium content should preferably be greater than or equal to 0.01% in order to control the growth of the grain at high temperature and to facilitate hot processing. Niobium is indeed a growth inhibitor to limit the germination of crystallization and grain growth in conjunction with parboiling.

The alloy contains a little carbon so that, during the preparation, the deoxidation is sufficient, but the carbon content must remain less than 0.1% and preferably less than 0.02% or even 0, 01% to avoid forming too many carbides which deteriorate the magnetic properties.

There is no lower limit defined for the contents of elements such as Mn, Si, Ni or Cr. These elements may be absent, but they are generally present at least in very small quantities as a result of their presence in the raw materials or as a result of pollution by refractory furnace development. These elements have no influence on the magnetic properties of the alloy when they are present in very small quantities. When their presence is significant, it is because they have been added voluntarily to adjust the magnetic properties of the alloy to the intended application.

This alloy is for example the alloy known as AFK 502R which contains essentially 49% cobalt, 2% vanadium and 0.04% niobium, the remainder consisting of iron and impurities and small quantities of elements such as C, Mn, Si, Ni and Cr.

This alloy is produced in a manner known per se and cast in the form of semi-finished products such as ingots. To make a thin strip, a semi-finished product, such as an ingot, is hot rolled to obtain a hot strip whose thickness depends on the practical conditions of manufacture. As an indication, this thickness is generally between 2 and 2.5mm. At the end of hot rolling, the resulting strip is subjected to a quenching. This treatment largely avoids the order / disorder transformation in the material so that it remains in an almost disordered structural state, little changed with respect to its structural state at a temperature above 700 ° C and which therefore, is sufficiently ductile to be cold rolled. The hypertrempe therefore allows the hot strip to be then cold rolled without clutter up to the final thickness. The quenching can be carried out directly at the hot rolling outlet if the rolling end temperature is sufficiently high, or, otherwise, after reheating to a temperature above the order / disorder transformation temperature. In practice, the weakening order is established between 720 ° C and ambient, the metal is violently cooled, for example water (typically at a speed greater than 1000 ° C / min), at the output of hot rolling from a temperature of 800 to 1000 ° C to ambient, the hot rolled metal then slowly cooled, so fragile, is heated to between 800 and 1000 ° C before violent cooling to ambient . Such a treatment is known in itself to the skilled person who knows how to make it on the equipment that he usually has.

After hardening, the hot strip is cold rolled to obtain a cold strip having a thickness of less than 1 mm, preferably less than 0.6 mm, generally of between 0.5 mm and 0.2 mm, and which can be as low as at 0.05 mm.

After having manufactured the cold-rolled cold-rolled strip, it is subjected to annealing in a passage furnace at a temperature such that the alloy is in a disordered ferritic phase. This means that the temperature is between the order / disorder transformation temperature and the ferritic / austenitic transformation temperature. For an iron-cobalt alloy having a cobalt content of between 45 and 55% by weight, the annealing temperature should be between 700 ° C and 930 ° C. The range of temperature of the annealing at the parade can be all the more extended towards the low temperatures that the cobalt content will approach 18%. For example, at 27% cobalt, the annealing temperature should be between 500 and 950 ° C. The person skilled in the art knows how to determine this annealing temperature according to the composition of the alloy.

The rate of passage in the oven can be adapted taking into account the length of the oven so that the passage time in the homogeneous temperature zone of the oven is less than 10 minutes and preferably between 1 and 5 minutes. In any case, the holding time at the treatment temperature must be greater than 30s. For an industrial furnace with a length of about one meter, the speed must be greater than 0.1 meters per minute. For another type of industrial furnace 30 m long, the speed of movement must be greater than 2 meters per minute, and preferably 7 to 40m / min. In a general manner, the skilled person knows how to adapt the scrolling speeds according to the length of the furnaces which he has.

It should be noted that the treatment furnace used can be of any type. In particular, it may be a conventional resistance furnace or a thermal radiation furnace, a Joule annealing furnace, a fluidised bed annealing plant or any other type of furnace.

At the furnace outlet, the strip must be cooled at a fast enough speed to avoid a complete order-disorder transformation. However, the inventors were surprised to note that, unlike a strip of 2 mm thick which must be hyper-tempered to then be cold rolled, a thin strip (0.1 to 0.5 mm) intended to be machined , stamped, punched may be subject only to a partial ordering which results in a weak degree of fragility so that a hyperemperature is not necessary.

The inventors have also been surprised to find that after an annealing at the parade as just described, the cutability of the band becomes very good when the transformation disorder / order is not total. This means, unexpectedly, that such a band can be cut by mechanical means despite a partial ordering generating a certain degree of fragility.

For the disorder / order transformation is not total, the cooling rate - determined between the order / disorder temperature (700 ° C for a conventional alloy of composition close to Fe-49% Co-2% V) and 200 ° C - must be greater than 600 ° C per hour, and preferably greater than 1000 ° C per hour or even 2000 ° C / h. In practice, it is not necessary to exceed 10,000 ° C / h and a speed of between 2,000 ° C / h and 3,000 ° C / h is generally sufficient.

The inventors have found, surprisingly, that with such a run-off treatment, and contrary to what is observed with static heat treatments making it possible to obtain comparable mechanical or magnetic properties, sufficiently ductile strips were obtained in order to be able to be cut mechanically to make parts to be stacked to form magnetic yokes or other magnetic components.

The inventors have also found that by adjusting the passage time in the oven it is possible to adjust the mechanical characteristics obtained on the strip so that, from a standard iron-cobalt alloy, it is possible to obtain both alloys with usual mechanical characteristics, that is to say with a yield strength of between 300 and 500 MPa, as alloys of the high yield strength (HLE) type, that is to say having a yield strength greater than 500 MPa, preferably from 600 to 1000 MPa, and up to 1200 MPa. Of course, these heat treatments lead to magnetic properties that are very different, in particular with regard to the magnetic losses. The standard iron-cobalt alloy is for example an iron-cobalt alloy of the AFK 502R type containing essentially 49% of cobalt, 2% of vanadium and 0.04% Nb, the remainder being iron and impurities,

The inventors have found that this set of unusual performances, namely cutability in the annealed state, while at the same time fixing the elastic limit between 300 and 1200 MPa, was closely related to the particular metallurgical structure obtained by the continuous annealing according to the invention. which is different from the metallurgical structure resulting from static annealing. This concerns in particular the rate of crystallization and, for sufficiently crystallized materials, the distribution of grain sizes, which is very different from that obtained with static annealing to obtain the same properties of use of the material. .

We will now describe more precisely the effects of heat treatment on the runway and its conditions of realization on the mechanical and magnetic properties of an alloy of the 50% Cobalt type, from a series of tests.

On the one hand, laboratory tests were performed on an alloy of non-standard composition AFK502NS (Casting JB 990) which contains 48.6% Co-1.6% V-0.119% Nb-0.058% Ta-0.012% C, the remainder being iron and impurities and in a conventional alloy grade AFK 502 R (casting JD173) ie a standard alloy containing 48.6% Co-1.98% V-0, 14% Ni-0.04% Nb-0.007% C. The rest being iron and impurities. These alloys, which were first manufactured in the form of cold-rolled strips of thickness 0.2 mm, were subjected to heat treatments on passage through a hot oven with a one-minute hold at a temperature of 785 ° C. C, 800 ° C, 840 ° C and 880 ° C respectively. These heat treatments, which make it possible to simulate a heat treatment on the industrial runway, were carried out under Argon and were followed by rapid cooling at a speed of between 2,000 ° C./h and 10,000 ° C. more precisely 6000 +/- 3000 ° C / h taking into account the inaccuracy of the determination of this type of speed and the non-uniformity of the cooling rate between the bearing temperature and 200 ° C or the ambient. These tests made it possible to obtain the results reported in Table 1.

• T : est la température de recuit en °C
• B1600: est l'induction magnétique exprimée en Tesla, pour un champ magnétique de 1600 A/m (environ 20 Oe).
• Br/Bm : est le rapport de l'induction magnétique rémanente Br à l'induction magnétique maximale Bm obtenue à saturation magnétique de l'échantillon.
• Hc : est le champ coercitif en A/m
• Pertes : sont les pertes magnétiques en W/kg dissipées par les courants induits lorsque l'échantillon est soumis à un champ magnétique variable qui, dans le cas présent, est un champ alternatif de fréquence 400 Hz induisant une induction alternative sinusoïdale grâce à l'emploi d'un asservissement électronique du champ magnétique appliqué, ce qui est connu en lui-même de l'homme du métier ;
• la valeur maximale du champ magnétique est de 2 Tesla.
• R_P0,2 = est la limite d'élasticité conventionnelle mesurée en traction pure sur des échantillons normalisés.

Tableau 1 : effets du traitement thermique au défilé et de ses conditions de réalisation sur les propriétés mécaniques et magnétiques Nuance Coulée T (°C) B1600 (Tesla) Br/Bm Hc (A/m) Pertes (W/kg) R_P0,2 (MPa) 785 1,5850 0.83 822 339 990 800 1,6230 0.80 629 272 890 AFK502R (standard) JD173 840 1,7560 0.49 183 106 660 880 1,7500 0.40 130 85 600 785 1,5180 0.81 883,3 381 1090 AFK502NS (non standard) JB990 800 1,5490 0.80 779,96 336 970 840 1,7260 0.64 306,40 156 760 880 1,8080 0.45 148 95,5 620 In Table 1:

• T: is the annealing temperature in ° C
• B1600: is the magnetic induction expressed in Tesla, for a magnetic field of 1600 A / m (about 20 Oe).
• Br / Bm: is the ratio of the remanent magnetic induction Br to the maximum magnetic induction Bm obtained at magnetic saturation of the sample.
• Hc: is the coercive field in A / m
• Losses: are the magnetic losses in W / kg dissipated by the currents induced when the sample is subjected to a variable magnetic field which, in this case, is an alternating field of frequency 400 Hz inducing an induction sinusoidal alternative through the use of an electronic control of the applied magnetic field, which is known in itself to the skilled person;
• the maximum value of the magnetic field is 2 Tesla.
• R _P0,2 = is the conventional yield strength measured in pure tension on standardized samples.

<u> Table 1: effects of thermal treatment on the runway and its conditions of realization on the mechanical and magnetic properties </ u> Shade cast T (° C) B1600 (Tesla) Br / Bm Hc (A / m) Losses (W / kg) R _P0.2 (MPa) 785 1.5850 0.83 822 339 990 800 1.6230 0.80 629 272 890 AFK502R (standard) JD173 840 1.7560 0.49 183 106 660 880 1.7500 0.40 130 85 600 785 1.5180 0.81 883.3 381 1090 AFK502NS (non-standard) JB990 800 1.5490 0.80 779.96 336 970 840 1.7260 0.64 306.40 156 760 880 1.8080 0.45 148 95.5 620

After heat treatment, mechanical cutting tests were performed using punches and dies. It follows from these results that after annealing, it is possible to cut pieces in satisfactory conditions without any apparent sign of fragility as well with the non-standard shade composition AFK 502NS, as with the standard or standard shade AFK 502 R ,. It can also be seen that by adapting the annealing temperature to the defile between 785 ° C. and 880 ° C., it is possible to obtain mechanical properties of the high yield strength type, both for the AFK502NS alloy and for the AFK502R classic alloy and that the mechanical characteristics obtained are very comparable. As a result, it appears that it is not necessary to use two distinct shades to obtain alloys with a high yield strength type or alloys with a current yield strength, that is to say for manufacture alloy parts with a high yield strength or an alloy with a common yield strength.

Moreover, these results show that the magnetic properties, including the losses measured under an alternating field of maximum amplitude of 2 Tesla at a frequency of 400 Hertz, are quite comparable. Moreover, it can be seen that the relationship between magnetic losses and yield strength for sheets of thickness 0.20 mm, measured on washers cut in the annealed strip, are quite comparable for these 2 alloys of different composition.

On these materials, in the post-annealing state described above, a high temperature annealing called "static annealing optimization" was also performed to optimize the magnetic characteristics. This annealing was done on the washers in static annealing at a temperature of 850 ° for three hours. The results obtained with this static optimization annealing are reported in Table 2 below. <u> Table 2: magnetic properties after optimization annealing </ u> Shade cast T (° C) B at 1600 A / m (Tesla) Br / Bm Hc (A / m) Losses (W / kg) 2T-400 Hz AFK502R standard according to the invention 785 2.2110 0.69 51.7 36.0 800 2.2040 0.69 50.9 35.5 JD173 840 2.1970 0.66 50.9 35.0 880 2,2010 0.67 53.3 34.0 AFK502R standard without annealing, with standard static annealing 850 ° C JD173 850 2,225 0.71 0.70 36 AFK502NS non-standard according to the invention 785 2.2140 0.78 62.1 52.0 JB990 800 2.2040 0.74 58.9 53.5 840 2.2140 0.78 62.1 54.0 880 2.2190 0.79 62.9 51.0 AFK502R non-standard without annealing, with standard static annealing 850 ° C JB 990 850 2,244 0.79 1.1 52

In view of these results it can be seen that the magnetic losses at 400 Hertz under a field of 2 Tesla are considerably reduced and more generally that all the magnetic properties obtained do not depend substantially on the annealing temperature at the parade. These properties are moreover almost identical to the properties obtained on washers extracted from strips of thickness 0.2 mm which were not annealed at the runway, but which underwent the same static optimization annealing, which corresponds to the prior art.

These results show that the run-on annealing gives an advantage to the AFK 502 R type material (classic grade): in fact with this material it is possible to produce pre-annealed strips having HLE characteristics which, moreover, can be cut and formatted in this pre-annealed state
In addition, it is found that the compromise mechanical properties / magnetic properties can be adjusted by the annealing temperature parade. As a result, an alloy having the chemical composition of these examples can be used by a customer who wishes to manufacture both parts with high mechanical characteristics as well as with current mechanical characteristics and which can perform static optimization annealing only on the parts it has cut to simply optimize the magnetic losses if necessary.

In addition, a series of tests were carried out on industrial AFK 502R alloy strips of standard composition hardened to a thickness of 0.35 mm. During these tests, run-on annealing treatments were carried out at different rates of passage in an industrial furnace having a useful length of 1.2 m. Useful length means the length of the furnace in which the temperature is sufficiently homogeneous to correspond to the temperature step of the annealing.

The chemical compositions of the samples used are shown in Table 3. In this table, all the elements are not indicated and one skilled in the art will understand that the rest is iron and impurities resulting from the preparation, as well as any small quantities such as carbon. <u> Table 3: Chemical compositions of the samples used </ u> cast landmark Co V Nb mn Cr Yes Or # 1 JD842 48.61 1.99 0.041 0,027 0,015 0.016 0.04 # 2 JE686 48,49 2.00 0,037 0,042 0.031 0,061 0.10 # 3 JE798 48.01 1.99 0.041 0.043 0,040 0.057 0.16 # 4 JE799 48.51 1.96 0,040 0,035 0,028 0,051 0.06 # 5 JE872 48.45 1.98 0.041 0.043 0.049 0,069 0.14

The rates of passage were chosen so that each of these treatments corresponds to a time spent above 500 ° C, the beginning of the restoring temperature, substantially less than 10 minutes.

The runway annealing was done at three speeds of travel: 1.2 m per minute to obtain the magnetic and mechanical properties corresponding to the use to achieve magnetic stator yokes for which low to medium magnetic loss levels are sought. ; a speed of 2.4 m per minute to obtain the mechanical characteristics suitable for producing magnetic rotor yokes, and at 3.6 and 4.8 m per minute to obtain mechanical characteristics corresponding to the HLE quality. In addition, for comparison, samples were subjected to static annealing at a temperature of 760 ° C for two hours. This annealing is a conventional "static annealing optimization" type annealing which leads to properties comparable to that of run-on annealing at the rate of 1.2 m per minute at 880 ° C. Finally, for the highest runway annealing temperature (880 ° C), the run speed was further lowered (within a 10min step) to further reduce the magnetic losses and the yield strength. Indeed, for some applications, one can ask for magnetic losses to the stator low enough. These results show that this effectively makes it possible to reduce R _P0.2 below 400 MPa, which is interesting as an extended range of adjustment of the elastic limit by simple adjustment of the scrolling speed. On the other hand, the magnetic losses are not reduced with respect to the speed of neighboring value. Also, if we want to significantly reduce the magnetic losses, it is necessary to carry out an additional annealing static magnetic optimization as shown by the results in Table 2.

The results of the tests carried out with casting No. 1. JD 842 are reported in Table 4, the results obtained with the other flows being comparable.

These results show that the yield strength R _{P0,2 can be set} within a very wide range of values between 400 MPa and 1200 MPa by varying the annealing parameters which are the speed of passage, that is to say say the residence time high temperature, and the annealing temperature and this, under satisfactory conditions for industrial production. Indeed, the properties obtained vary slowly enough with the processing parameters to be able to control an industrial manufacturing. These results also show that there is a strong correlation between the elastic limit, the coercive field and the various other properties of the alloy.

Moreover, these tests made it possible to identify the effects of heat treatments on the metallographic structure of the alloy produced by the process according to the invention. The tests were carried out in particular on casting JD 842. The measurements were made in particular on a sheet having been annealed at the parade at 880 ° C with different speeds of scrolling. The temperature of 880 ° C was chosen because it is the one that corresponds to the optimum for obtaining good magnetic properties, that is to say, at a temperature allowing to obtain at the same time low values of magnetic losses and a wide range of elasticity limits (for example from 300 MPa to 800 MPa) by simple variation of the running speed with values leaving the alloy only a few minutes (<10 minutes) in the temperature plateau zone . <u> Table 4: Mechanical and magnetic properties according to the speed of scrolling during the annealing at the parade </ u> Conditions annealing parade DC current Losses (W / kg) at 400 Hz T _RD (° C) V (m / min) B1600 (Tesla) Br / Bm Hc (A / m) B = 1.5 Tesla B = 2 Tesla R _P0.2 (MPa) 1.2 1.6750 0.69 321 111 205 665 760 ° C 2.4 1.5400 0.83 907 252 420 1030 3.6 1.5250 0.84 939 264 443 1140 4.8 1.5250 0.84 907 255 414 1230 1.2 1.7700 0.48 127 65 125 540 785 ° C 2.4 1.7050 0.75 446 135 245 760 3.6 1.5300 0.83 915 255 430 1060 4.8 1.5300 0.86 915 260 432 1200 1.2 1.7350 0.46 122 66 125 540 810 ° C 2.4 1.7750 0.53 151 71 137 580 3.6 1.6400 0.76 549 163 286 830 4.8 1.5200 0.84 947 266 438 1140 1.2 1.7250 0.40 107 63 119 500 840 ° C 2.4 1.7600 0.47 117 65 121 530 3.6 1.7400 0.66 255 94 176 710 4.8 1.5400 0.81 820 230 382 1000 0.6 1,210 * 0.45 95 108 390 880 ° C 1.2 1.5050 * 0.45 94 95 435 2.4 1.5800 * 0.57 89 103 495 4.8 8,850 * 0.68 392 845 * B = For a field of 800 A / m
B1600 = Magnetic induction obtained for a magnetic field of 1600 A / m

To study the metallographic structures, micrographic observations were made on samples taken from the strips so that the slice of the rolled strips perpendicular to the rolling direction was observed. On these samples micrographs were made with an immersion attack for 5 seconds in a bath of iron perchloride at room temperature containing (per 100 ml): 50 ml of FeCl ₃ and 50 ml of water after polishing with 1200 paper then electrolytic polishing with a bath A2 consisting (for 1 liter) of 78 ml of perchloric acid, 120 ml of distilled water, 700 ml of ethyl alcohol, 100 ml of butylglycol.

These observations were made under an optical microscope with a magnification of 40. It has been found that for low annealing rates, i.e. 1.2 m per minute, the structure is similar to that observed on materials. having undergone static annealing. It is an Isotropic crystallized structure. For static annealing the structure is apparently 100% crystalline and the grain boundaries are perfectly defined. For runway annealing at 785 ° C, the structure is partially crystallized (the grain boundaries are not very well defined) and for annealing at 880 ° C, the structure is more crystalline but the grain boundaries are not however not sufficiently revealed to determine if these samples are 100% crystalline.

For the highest speeds, that is, for speeds of 2.4 m per minute, 3.6 m per minute and 4.8 m per minute, the micrographs show a very specific structure very distinct from the structures obtained by static annealing. It is a structure apparently close to that of the hardened metal. The inventors have also found that the micrographs made on the materials which were annealed at 880 ° C. at a speed of 4.8 m per minute had a very anisotropic structure (very elongated grains), much more anisotropic than the structure obtained by annealed at 785 ° C with a flow rate of 4.8 m per minute.

• d'une part une structure spécifique anisotrope obtenue pour les défilés aux vitesses les plus élevées (2,4 m par minute, 3,6 m par minute et 4,8 m par minute). Cette structure est une structure restaurée ou partiellement cristallisée ce qui peut être confirmé par un examen aux rayons X qui montre que la texture est celle d'un matériau restauré faiblement recristallisé, très similaire à la texture d'écrouissage ;
• d'autre part, une structure en apparence similaire à celle que l'on obtient par un recuit statique et qui correspond au recuit au défilé à faible vitesse (1,2 m par minute et 0,6 m par minute). Il s'agit d'une structure entièrement cristallisée ce qui est confirmé par un examen aux rayons X, avec une texture très proche de celle du métal recristallisé en recuit statique.

It thus appears that with heat treatments at the parade it is possible to obtain two types of structure:

• on the one hand, an anisotropic specific structure obtained for parades at the highest speeds (2.4 m per minute, 3.6 m per minute and 4.8 m per minute). This structure is a restored or partially crystallized structure which can be confirmed by an X-ray examination which shows that the texture is that of a restored weakly recrystallized material, very similar to the hardening texture;
• on the other hand, a structure apparently similar to that obtained by a static annealing and which corresponds to the annealing at low speed (1.2 m per minute and 0.6 m per minute). It is an entirely crystallized structure which is confirmed by an X-ray examination, with a texture very similar to that of the recrystallized metal in static annealing.

On these different samples the grain size was also determined. Since the coercive field of a magnetic alloy is closely related to the size of the grain, in order to be able to make meaningful comparisons between two modes of treatment of the same material, it is necessary to make observations on materials having equivalent coercive fields. Also, to carry out these measurements, samples with adjacent coercive fields were chosen, and measurements were made on a material which had been subjected to static annealing at 760 ° C for two hours, and on the other hand for a material which had been annealed in the parade at 880 ° C with a pass rate of 1.2 m per minute.

• les grains dont la surface va de 10 µm² à 140 µm² par pas de 10 µm².
• les grains dont la surface va de 140 µm² à 320 µm² par pas de 20 µm²,
• les grains dont la surface va de 320 µm² à 480 µm² par pas de 40 µm²,
• les grains dont la taille va de 480 à 560 µm², les grains dont la taille va de 560 à 660 µm², les grains dont la taille va de 660 à 800 µm², les grains dont la taille va de 800 à 1000 µm², les grains dont la taille va de 1000 à 1500 µm², puis les grains dont la taille dépasse 1500 µm².

The grading was done using automatic image analysis equipment to detect the grain boundary, calculate the perimeter of each of them, convert this perimeter to equivalent diameter and finally , to calculate the surface of the grain. This device also makes it possible to obtain a total number of grains as well as their surface. Such automatic grain size image analysis devices are known per se. In order to obtain results that have a satisfactory statistical significance, the rating was performed on a plurality of sample areas. The quotation was made by defining the following grain size classes:

• grains with a surface area ranging from 10 μm ² to 140 μm ² in steps of 10 μm ² .
• the grains whose surface ranges from 140 μm ² to 320 μm ² in steps of 20 μm ² ,
• grains whose surface ranges from 320 μm ² to 480 μm ² in steps of 40 μm ² ,
• grains ranging in size from 480 to 560 μm ² , grains ranging in size from 560 to 660 μm ² , grains ranging in size from 660 to 800 μm ² , grains ranging in size from 800 to 1000 μm ² , the grains whose size ranges from 1000 to 1500 μm ² , then the grains whose size exceeds 1500 μm ² .

These examinations show that static annealing at 760 ° C is characterized by a Gaussian distribution of grain size with a peak around 150 μm ² . Grains of this size represent 5.5% of the total area of a sample analyzed. There is very little coarse grain and the grain size is less than 750 μm ² .

On the other hand, continuously annealed materials show a structure in which there are fewer small grains but larger grains between 200 and 1000 μm ² . In particular, the grains between 30 and 50 μm ² occupy a surface equivalent to that occupied by large grains of size between 500 μm ² and 1100 μm ² .

These results show that, although apparently comparable to a structure obtained by static annealing, continuous annealing leads to a very different structure, in particular by the distribution of grain sizes.

In addition, grain gradings were carried out on four 0.34 mm thick strips on which on the one hand an annealing was carried out at 880 ° C. under hydrogen at a speed of 1.2 m per minute and on the other hand a static annealing optimization at 760 ° C for two hours under Hydrogen. These bands correspond to the castings JE 686, JE798, JD 842, JE 799 and JE 872 whose compositions are reported in Table 3. These examinations show that for these flows, the distribution of the finest grains and especially less than 80 μm in size ² is very different for samples that have been static annealed at 760 ° C than for samples that result from a run-on treatment at 880 ° C. In particular, the fine grains are much more numerous on the samples which have been subjected to a static annealing than on the samples which have been subjected to a parade annealing. It should be noted in particular that for grains smaller than 40 μm ² , the number of grains, by size class, on the samples having undergone static annealing is greater than the maximum number of grains obtained on samples annealed at the parade. All of these results show that, especially with runway annealing, the grain size distribution does not have a dominant grain size. The maximum number of grains recorded in a grain size class never exceeds 30, unlike static annealing where the number of grains can reach 160 for the same size class, especially for small grains.

For each of these samples, the total number of grains for an area of 44,200 mm ² and the average grain size were also determined. These results are shown in Table 5. <u> Table 5: Size and number of grains obtained for various compositions </ u> cast annealing Average grain size (μm ² ) Total number of grains JD842 Static 760 ° C / 2h 94 454 Parade 880 ° C / 1.2m / min 155 260 JE686 Static 760 ° C / 2h 104 332 Parade 880 ° C / 1.2m / min 175 204 JE872 Static 760 ° C / 2h 58 563 Parade 880 ° C / 1.2m / min 145 243 JE798 Static 760 ° C / 2h 51 634 Parade 880 ° C / 1.2m / min 168 211 JE799 Static 760 ° C / 2h 78 427 Parade 880 ° C / 1.2m / min 127 243

• soit la structure est du type « partiellement cristallisée », c'est-à-dire que, sur au moins 10% de la surface d'échantillons observés au microscope avec un grossissement de x 40 après attaque chimique au perchlorure de fer, il n'est pas possible d'identifier des joints de grain ;
• soit la structure est du type « cristallisée », c'est-à-dire que sur au moins 90% de la surface d'échantillons observée au microscope avec un grossissement de x 40 après attaque chimique au perchlorure de fer, il est possible d'identifier un réseau de joints de grains et, dans la plage des tailles de grain allant de 0 à 60 µm², il existe au moins une classe de 10 µm² de largeur de taille de grains comprenant au moins deux fois plus de grains que la même classe de taille de grains correspondant à l'observation d'une bande laminée à froid de comparaison ayant la même composition, n'ayant pas été soumise à un recuit continu mais ayant été soumise à un recuit statique à une température telle que l'écart entre champ coercitif obtenu avec le recuit statique et le champ coercitif obtenu avec le recuit au défilé est inférieur à la moitié de la valeur du champ coercitif obtenu par le traitement au défilé et, dans la plage de taille de grains allant de 0 à 60 µm², il existe au moins une taille de classe de grains de 10 µm² de largeur dont le rapport du nombre de grains au nombre total de grains observés sur l'échantillon ayant subi un recuit au défilé est supérieur d'au moins 50% au même rapport correspondant à un échantillon prélevé sur la bande laminée à froid de comparaison ayant subi un recuit statique.

These results make it possible, in particular, to show that the samples having been subjected to a run-on annealing at 880 ° C. with a speed of 1.2 m / m per minute have an average grain size of greater than 110 to ² μm and an average number less than 300 samples, whereas the samples having been subjected to static annealing at 760 ° C. for two hours have mean grain sizes of less than 110 μm ² and a number of grains greater than 300. These characteristics make it possible to identify or to clearly distinguish the structures obtained on the one hand by annealing to the parade, and on the other hand by static annealing. More generally, the inventors have found that the types of treatment can be distinguished by the following grain size characteristics:

• either the structure is of the "partially crystallized" type, that is to say that, on at least 10% of the surface of samples observed under a microscope with a magnification of x 40 after chemical attack with iron perchloride, it is it is not possible to identify grain boundaries;
• either the structure is of the "crystallized" type, that is to say that on at least 90% of the surface of samples observed under a microscope with a magnification of x 40 after chemical attack with iron perchloride, it is possible to to identify a network of grain boundaries and, in the range of grain sizes from 0 to 60 μm ² , there is at least one class of 10 μm ² grain size width comprising at least twice as many grains as the same size class of grains corresponding to the observation of a comparative cold rolled strip having the same composition, not having been continuously annealed but having been subjected to static annealing at a temperature such that The difference between the coercive field obtained with the static annealing and the coercive field obtained with the parboiled annealing is less than half the value of the coercive field obtained by the parcel treatment and, in the grain size range from 0 to 60 μm ² , there is at least a grain class size of 10 μm ² in width, the ratio of the number of grains to the total number of grains observed on the sample having been annealed at least 50% more than at the same ratio corresponding to a sample taken from the static annealed cold rolled comparison strip.

On these samples we also made cutting tests. For this purpose stators were cut on samples which, according to the invention, were annealed at temperatures of 785 ° C., 800 ° C., 840 ° C., with travel speeds of 1.2 m per hour. minute for a useful oven length of 1.2 m, which corresponds to a residence time of one minute at the annealing temperature. These cuts were made on punched industrial punching plants using a punch and a die. The cuts were made on the strips of thickness of 0.20 mm and 0.35 mm.

The quality of the cut was determined by evaluating the cutting radius and the presence or absence of burrs. The results are shown in Table 6. On reading, it appears that whatever the thickness and regardless of the annealing temperature on the parade, the quality of the cut is satisfactory according to the usual criteria corresponding to the requirements of the customers. <u> Table 6: Cutting tests </ u> cast Thickness (mm) Annealing temperature Hardness Hv0.2 Cutting radius compared to the hardened state burr Customer validation JD414 0.20 mm 785 ° C 185 RAS RAS Okay 800 ° C 180 RAS RAS Okay 840 ° C 173 RAS RAS Okay 0.35 mm 785 ° C 179 Superior Close to the job Okay 800 ° C 176 Less pronounced Higher than hard Okay 840 ° C 172 Less pronounced Higher than hard Okay

In Table 6, "close to hard" means that the number of burrs is substantially equal to or even slightly greater than the number of burrs found in the hardened state, while "greater than hard" means that the number of burrs is Burr is still slightly higher, while remaining acceptable according to the usual criteria corresponding to customer requirements.

The deformations after heat treatment of quality on the cut pieces were also examined.

Indeed, for some parts and especially for E-shaped parts, it is found that the final treatment performed on parts obtained by a method according to the prior art can lead to deformations that probably result from recrystallization and transformation. of the rolling texture in recrystallization texture. These deformations lead to dimensional variations of the order of a few tenths of a millimeter, which are not acceptable. For profiles in E for example where the legs of the E have a length of several tens of cm, which is large compared to the other dimensions of the E, after optimization annealing variations of spacing of neighboring legs are observed which are the order of 1 to 5mm between upper and lower legs.

In contrast, with the run-annealed alloy according to the present invention and which is in a crystallized or partially crystallized state, an additional static annealing of optimization of the magnetic properties - typically at 850 ° C for three hours - did not occur. in general no significant impact on the geometry of the pieces. Tests on parts in E have shown that the dimensional variations resulting from the static annealing of magnetic optimization remain less than 0.05 mm in the previous example of E-profiles, which is quite acceptable.

To clarify the roles of the annealing temperature and the cooling rate of the strip at the outlet of the treatment furnace, tests were carried out on a conventional grade AFK 502 R alloy containing 48.63% Co - 1.98% V - 0.14% Ni - 0.04% Nb - 0.007% C (Casting JD173), the remainder being iron and impurities.

This alloy was manufactured in the form of strips of different cold-rolled thicknesses, and then subjected to run-on annealing by passing at a continuous speed in a furnace under a protective atmosphere, at a plateau temperature of 700 ° C., 750 ° C. C, 800 ° C, 850 ° C, 900 ° C or 950 ° C, for a plateau time equal to 30 s, 1 min, or 2 min.

After this annealing, the strips were cooled to a temperature below 200 ° C at cooling rates between 600 ° C / h and 35000 ° C / h.

In addition, for comparison, some bands were cooled at a cooling rate of only 250 ° C / hr.

The ability to cut the annealed strips, and more generally their fragility with respect to the operations of implementation, including shaping, was tested by cutting traction specimens and washers of internal diameters and 26mm and 35mm respectively in the thin strips obtained after cooling.

The specimens were subjected to a standard tape fragility test in accordance with IEC 404-8-8. This test consists in bending the flat specimen at 90 ° alternatively from each initial position, according to a device and a procedure described in the ISO7799 standard. The bending radius chosen by the IEC 404-8-8 standard for extra-thin sheets (FeCo type) used at medium frequencies is 5mm. A 90 ° bend from the initial position with return to the home position counts as one unit. The test is stopped at the appearance of the first crack visible to the naked eye in the metal. The last folding is not counted. The tests were carried out at 20 ° C. on widgets of width 20 mm in FeCo alloy, by a slow and uniform movement of alternating folding.

These tests were stopped at 20 bends. Thus, a number of plies equal to 20 means that the corresponding sample withstands at least 20 bends.

In parallel, the samples in the form of plates were subjected to a cutting test on punched industrial punching plants using a punch and a die. The quality of the cut was determined by evaluating the cutting radius and examining the wafer for the burrs and the proportion of thickness of the metal that yielded by transgranular fracture without significant plastic elongation of the material (origin of the cutting burrs). ).

From these tests, the cutability of these samples was qualified as very good (TB), good (B), average (MO) or poor (MA).

A very good cutability corresponds to a metal cut with a reduced press force compared to what was known in the state of the art on a hardened FeCo alloy, to a cutting zone without smudge and to a high proportion of transgranular rupture thickness.

Good cutability corresponds to a metal cut with a high press force and in accordance with what was known in the state of the art on a FeCo alloy. In this metallurgical state (hardened or even slightly restored) the band is very elastic and strong and deforms widely before the punch begins its penetration, and as during penetration with a very large press force. The cutting zone is made by completely transgranular rupture without burr with a very large elastic return of the band after perforation.

A medium cutability is an alloy for which cutting is easy but the cutting area becomes irregular and burrs or tearing of metal appear on the exit face of the punch.

Cutability is described as bad when cracks appear around the punch before the punch has finished puncturing the sheet. The beginning of elastic pressure of the band by the punch may be sufficient to cause cracking and rupture of the sample.

On these materials, in the post-annealing state described above, a high temperature annealing called "static annealing optimization" was also performed to optimize the magnetic characteristics. This annealing was done on the washers static annealing at a temperature of 850 ° C for three hours

• t_p est le temps de palier en min,
• e est l'épaisseur de la bande en mm,
• T est la température de recuit en °C,
• V_R est la vitesse de refroidissement jusqu'à une température inférieure à 200 °C en °C/h,
• Hc est le champ coercitif en A/m,
• Nplis est le nombre de plis avant la casse,
• Déc. est la découpabilité,
• R_p0.2 est la limite d'élasticité conventionnelle mesurée en traction pure sur des échantillons normalisés, en MPa,
• Pertes (1) sont les pertes magnétiques en W/kg dissipées par les courants induits lorsque l'échantillon est soumis à un champ magnétique variable qui, dans le cas présent, est un champ alternatif de fréquence 400 Hz induisant une induction alternative sinusoïdale grâce à l'emploi d'un asservissement électronique du champ magnétique appliqué, connu en lui-même de l'homme du métier, dont la valeur maximale est de 2 Tesla. Dans le cas (1), le métal n'a subi que le recuit au défilé.
• Pertes (2) sont les pertes magnétiques en W/kg après le recuit d'optimisation, postérieur au recuit au défilé.

Tableau 7 : Effet de la température de recuit et de la vitesse de refroidissement de la bande en sortie du four sur les propriétés mécaniques et magnétiques N° t_p (min) e (mm) V_R (°C/h) T (°C) Hc (A/m) Nplis Déc. R_p0.2 (MPa) Pertes (W/kg) à 400 Hz (1) (2) 1 1 0,2 35 000 700 1512 >20 B 1270 590 35 2 1 0,2 35 000 750 1114 >20 TB 1030 445 34,5 3 1 0,2 35 000 800 796 >20 TB 850 335 35 4 1 0,2 35 000 850 175 >20 TB 490 123 34,5 5 1 0,2 35 000 900 143 >20 TB 470 108 37 6 1 0,2 35 000 950 271 >20 TB 540 146 44 7 1 0,2 5000 700 1512 >20 B 1250 575 35,5 8 1 0,2 5000 750 955 >20 TB 920 398 36 9 1 0,2 5000 800 716 >20 TB 810 302 34 10 1 0,2 5000 850 159 >20 TB 480 101 34,5 11 1 0,2 5000 900 127 >20 TB 460 87 35 12 1 0,2 5000 950 255 >20 TB 520 142 42 13 1 0,2 1 000 800 581 >20 TB 725 262 34,5 14 1 0,2 600 800 406 17 MO 622 193 34 15 1 0,2 600 850 143 15 MO 463 105 35 16 1 0,2 250 700 1194 >20 B 1150 513 34,5 17 1 0,2 250 750 279 7 MA 540 152 34 18 1 0,2 250 800 199 4 MA 500 129 35 19 1 0,2 250 850 127 3 MA 460 85 35 20 1 0,2 250 900 103 4 MA 430 80 38 21 1 0,2 250 950 191 4 MA 490 125 45 22 1 0,35 35 000 800 915 >20 TB 910 432 71 23 1 0,35 5000 800 772 >20 TB 830 369 70,5 24 1 0,35 250 800 223 3 MA 505 159 71 25 1 0,1 35 000 800 676 >20 TB 795 274 28 26 1 0,1 5000 800 581 >20 TB 730 241 27,5 27 1 0,1 250 800 1432 3 MA 470 79 28 28 0,5 0,2 5000 800 1353 >20 B 1180 535 24,5 29 0,5 0,2 600 800 836 5 MA 880 344 35,5 30 2 0,2 5000 800 302 >20 TB 560 161 35 31 2 0,2 250 800 119 4 MA 450 84 34,5 32 0,5 0,35 5000 800 1432 >20 B 470 519 71,5 33 0,5 0,35 250 800 931 5 MA 920 442 71 34 2 0,35 5000 800 326 >20 TB 590 199 71,5 35 2 0,35 250 800 143 4 MA 475 131 71,5 These tests made it possible to obtain the results reported in Table 7, in which:

• t _p is the dwell time in min,
• e is the thickness of the strip in mm,
• T is the annealing temperature in ° C,
• V _R is the cooling rate to a temperature below 200 ° C in ° C / h,
• Hc is the coercive field in A / m,
• Nplis is the number of folds before breaking,
• Dec. is the cutability,
• R _p0.2 is the conventional yield strength measured in pure tension on standardized samples, in MPa,
• Losses (1) are the magnetic losses in W / kg dissipated by the currents induced when the sample is subjected to a variable magnetic field which, in the present case, is an alternating field of frequency 400 Hz inducing a sinusoidal induction induction thanks to the use of an electronic control of the applied magnetic field, known in itself to the skilled person, whose maximum value is 2 Tesla. In the case (1), the metal has only undergone annealing.
• Losses (2) are the magnetic losses in W / kg after the optimization annealing, after the annealing at the parade.

<u> Table 7: Effect of Annealing Temperature and Cooling Speed of the Oven Strip on Mechanical and Magnetic Properties </ u> No. t _p (min) e (mm) V _R (° C / h) T (° C) Hc (A / m) Nplis Dec. R _p0.2 (MPa) Losses (W / kg) at 400 Hz (1) (2) 1 1 0.2 35,000 700 1512 > 20 B 1270 590 35 2 1 0.2 35,000 750 1114 > 20 TB 1030 445 34.5 3 1 0.2 35,000 800 796 > 20 TB 850 335 35 4 1 0.2 35,000 850 175 > 20 TB 490 123 34.5 5 1 0.2 35,000 900 143 > 20 TB 470 108 37 6 1 0.2 35,000 950 271 > 20 TB 540 146 44 7 1 0.2 5000 700 1512 > 20 B 1250 575 35.5 8 1 0.2 5000 750 955 > 20 TB 920 398 36 9 1 0.2 5000 800 716 > 20 TB 810 302 34 10 1 0.2 5000 850 159 > 20 TB 480 101 34.5 11 1 0.2 5000 900 127 > 20 TB 460 87 35 12 1 0.2 5000 950 255 > 20 TB 520 142 42 13 1 0.2 1,000 800 581 > 20 TB 725 262 34.5 14 1 0.2 600 800 406 17 MO 622 193 34 15 1 0.2 600 850 143 15 MO 463 105 35 16 1 0.2 250 700 1194 > 20 B 1150 513 34.5 17 1 0.2 250 750 279 7 MY 540 152 34 18 1 0.2 250 800 199 4 MY 500 129 35 19 1 0.2 250 850 127 3 MY 460 85 35 20 1 0.2 250 900 103 4 MY 430 80 38 21 1 0.2 250 950 191 4 MY 490 125 45 22 1 0.35 35,000 800 915 > 20 TB 910 432 71 23 1 0.35 5000 800 772 > 20 TB 830 369 70.5 24 1 0.35 250 800 223 3 MY 505 159 71 25 1 0.1 35,000 800 676 > 20 TB 795 274 28 26 1 0.1 5000 800 581 > 20 TB 730 241 27.5 27 1 0.1 250 800 1432 3 MY 470 79 28 28 0.5 0.2 5000 800 1353 > 20 B 1180 535 24.5 29 0.5 0.2 600 800 836 5 MY 880 344 35.5 30 2 0.2 5000 800 302 > 20 TB 560 161 35 31 2 0.2 250 800 119 4 MY 450 84 34.5 32 0.5 0.35 5000 800 1432 > 20 B 470 519 71.5 33 0.5 0.35 250 800 931 5 MY 920 442 71 34 2 0.35 5000 800 326 > 20 TB 590 199 71.5 35 2 0.35 250 800 143 4 MY 475 131 71.5

• un nombre de plis supérieur ou égal à 20 obtenu suite à un recuit au défilé à une température de palier supérieure ou égale à 720°C avec un temps de palier supérieur à 30 secondes est associé à une très bonne découpabilité (essais 2-6, 8-13) ;
• un nombre de plis supérieur ou égal à 20 obtenu suite à un recuit au défilé à une température de palier inférieure à 720°C ou un temps de palier inférieur ou égal à 30 secondes est associé à une bonne découpabilité (essais 1, 7, 16, 28, 32) ;
• un nombre de plis compris entre 15 et 20 est associé à une découpabilité moyenne, encore admissible ;
• un nombre de plis inférieur à 15 est associé à une découpabilité mauvaise, à éviter.

From these tests, the following experimental relationship has been demonstrated, associating the number of folds before breaking and the press-cutting ability of the materials:

• a number of folds greater than or equal to 20 obtained following a pass annealing at a plateau temperature greater than or equal to 720 ° C. with a step time of greater than 30 seconds is associated with a very good cutability (tests 2-6, 8-13);
• a number of folds greater than or equal to 20 obtained following run-in annealing at a plateau temperature of less than 720 ° C or a plateau time of less than or equal to 30 seconds is associated with good cutability (tests 1, 7, 16 , 28, 32);
• a number of plies between 15 and 20 is associated with an average cutability, still acceptable;
• a number of folds less than 15 is associated with poor cutability, to avoid.

Thus, only the conditions making it possible to obtain "medium" to "very good" cut-offs, hence materials having supported at least 15 successive bends without breaking, are retained.

Moreover, these tests show that, surprisingly, the cooling rate at the outlet of the annealing outlet controls the cutting ability of the annealed strip, and more generally its fragility with respect to the operations of implementation, the critical limit is around 600 ° C / h.

In addition, the following points appear.

At high cooling rates (35000 and 5000 ° C / h) the metal has systematically at least good cutability, or very good for partially or completely recrystallized materials, ie subjected to annealing temperatures at the runway. at least 710 ° C. Below 710 ° C. (tests 1 and 7), it would also be possible, by increasing the dwell time, to obtain a partial recrystallization, but this dwell time should be of long duration, very little compatible with annealing at room temperature. industrial fashion show. An annealing temperature above 700 ° C, or even above 720 ° C, is therefore favorable.

At 1000 ° C / h and especially 600 ° C / h, the cutability deteriorates, but it is still sufficient. However, in all cases tested at 250 ° C / h, the band breaks after a very small number of folds (often less than 5), which clearly shows that the materials then become fragile and uncutable.

It is considered that a cooling of at least 600 ° C / h makes it possible to obtain a satisfactory band of cutability.

This control of the cutability by control of the cooling rate at the annealing outlet at the industrial run is confirmed not only for a 0.2mm band thickness, but also for thicknesses of 0.1mm and 0.35mm, leading to the same ductile / brittle limit for a speed of about 600 ° C / h.

For short dwell times, less than 3 min, and annealing temperatures below 720 ° C (tests 1, 7 and 16), the coercive fields of the materials obtained are very high, at least 15 Oe, which corresponds to materials mainly hardened and restored, without significant crystallization. Nevertheless, the magnetic losses exceed 500 W / kg. It is therefore preferable to apply bearing temperatures greater than or equal to 720 ° C., making it possible to obtain, for bearing times of less than 3 minutes, limited magnetic losses (less than 500 W / kg for a thickness of 0.2mm).

Thus, the magnetic strips according to the invention advantageously have, for a thickness of between 0.05 mm and 0.6 mm, magnetic losses of less than 500 W / kg, preferably less than 400 W / kg.

It is also noted that incursions at too high temperatures in the austenitic range by annealing (annealing temperatures greater than 900 ° C., tests 6, 12 and 21) significantly degrade the magnetic losses after additional annealing at 850 ° C. / 3h. Also the parade annealing is more efficient if their bearing temperature is sufficiently far from 950 ° C.

Annealing at 900 ° C. does not modify magnetic losses little or little after additional static annealing of 3 hours compared with lower temperatures. Thus, the most relevant bearing temperature zone is between 720 ° C. and 900 ° C.

Furthermore, in addition to the important criterion of resistance to cutting annealed sheets, it is also important to produce magnetic materials having limited magnetic losses as regards both the energy efficiency aspects of the machines and the localized thermal heating aspects. .

Two points are thus to be distinguished.

In particular, the method according to the invention makes it possible to directly obtain products (such as stators or rotors) cut from the annealed strip, already having the desired HLE type mechanical performances with the necessarily degraded magnetic losses which correspond to them. . However, the magnetic losses must remain at a level that can remove the heat to the rotor: typically the magnetic losses at 2T / 400Hz for a thickness of 0.2mm must be less than 500W / kg, and preferably less than 400 W / kg. The method according to the invention makes it possible to achieve such values.

Moreover, while the method according to the invention makes it possible to cut all the parts in the annealed state of annealing with a predetermined and high elastic limit, for example according to the requirements of the rotor, it is necessary to apply after cutting , specifically to the stator cut pieces, an annealing of optimization of the magnetic properties (of the 850 ° C-3h type under pure H ₂ ), the stator needing generally and mainly very low magnetic losses. However, it is important that the strips supplied after runway annealing can restore, after additional optimization annealing, the same very low magnetic losses that they would have had directly by the only optimization annealing. These very low losses are of the order of 35 W / kg at 2T / 400Hz for a strip thickness of 0.2 mm, 71 W / kg for a strip thickness of 0.35 mm and 28 W / kg for a thickness of strip 0.1mm in the case of industrial and commercial grades Fe-49% Co-2% V -0-0.1% Nb -0.003 to 0.02% C not Revised after a ^1st development ingot. Thus, it is desirable that after application of an additional annealing of 850 ° C / 3h to the bands resulting from the annealing at the parade, the losses do not exceed by more than 20% the magnetic losses which are measured at the end of a single "conventional" static annealing of 850 ° C / 3h. The method according to the invention also makes it possible to achieve such performances.

To study the potential influence of alloy composition on mechanical and magnetic properties, similar tests to those described with reference to Table 7, for various alloy compositions. For these tests, the run-on annealing was carried out at 850 ° C., with a dwell time of 1 min, and followed by cooling at 5000 ° C./h, under H ₂ .

The chemical compositions of the samples used, as well as the properties obtained, are reported in Table 8. In this table, Js denotes the saturation magnetization, expressed in Tesla. <u> Table 8: Influence of the composition on the mechanical and magnetic properties (1) </ u> Sample AT B VS D E F BOY WUT H VS 0,007 0.012 0,009 0,008 0.093 0,011 0,008 0,017 mn 0,024 0,042 0,037 0.23 0.1 0,023 0.23 0.16 Yes 0,045 0,037 0.42 0.09 1.7 0.062 0.09 0.31 S 0.0021 0.0027 0.0075 0.0021 0.0018 0.0017 0.0021 0.0016 P 0.0033 0.0025 0.0028 0.0041 0.0023 0.0035 0.0041 0.0026 Or 0.14 0.18 0.12 0.09 0.08 0,022 0.09 3.7 Cr 0,026 0,036 0,032 0,017 0.67 0.012 0,017 0.32 MB <0.005 <0.005 <0.005 <0.005 <0.005 <0.005 <0.005 <0.005 Cu 0,011 0.01 0.088 0.033 0,037 0,026 0.033 0,027 Co 48.63 48.61 48.52 50.05 27,05 48.72 50.05 48.69 V 1.98 1.59 2.03 0.98 0.04 1.55 1.4 1.92 al <0.005 <0.003 <0.004 <0.004 <0.004 <0.004 <0.004 <0.004 Nb 0.04 0.119 0.31 0.006 0.16 0,003 0.006 0.04 Ti <0.005 0.0015 0,009 0.0013 <0.0005 <0.005 0.0013 0.0015 N ₂ 0.0046 0.0027 0.0017 0.0034 0.0038 0.0043 0.0034 0.0048 Your <0.0008 0.058 0,032 0,032 <0.0008 <0.0008 <0.0008 <0.0008 Zr <0.0008 <0.0008 <0.0008 <0.0008 <0.0008 <0.0008 0.32 <0.0008 B <0.0006 <0.0005 0.005 0.04 <0.0006 <0.0006 0.0007 0.0013 Fe 48.9 49.1 47.915 48,15 71.94 48.56 47.74 44.8 W <0.005 <0.005 <0.005 <0.005 <0.005 0.6 <0.005 <0.005 Js (T) 2.35 2.36 2.32 2.37 2.28 2.34 2.36 2.26 Hc (A / m) 159 541 668 772 414 151 271 127 Nplis > 20 > 20 > 20 > 20 > 20 > 20 > 20 > 20 Dec. TB TB TB TB TB TB TB TB R0.2 (MPa) 480 845 960 1045 625 530 640 530 Losses (W / kg) at 400 Hz (1) 101 245 295 334 197 102 146 93 Losses (W / kg) at 400 Hz (2) 34.5 38 42 45 81 36 38.5 33 Inv? YES YES YES YES YES YES YES YES

All the compositions of this table are in accordance with the invention.

Example A corresponds to an alloy of the same composition as that used for the tests given in Table 7. Example A is identical to Test 10 of Table 7.

Example B includes a decrease in the percentage of vanadium and additions of niobium and tantalum, the latter being used to replace the role of moderator of the ordering of vanadium, while niobium is a growth inhibitor to limit germination of recrystallization and grain growth in conjunction with runway annealing. It can thus be seen that the performances are in the range of the properties concerned and at the same time shifted towards higher elastic limits and magnetic losses compared with Example A.

Example C contains more Si, S, Nb, Ta and B than the reference alloy A while being consistent with the target range of properties: the silicon added moderately hardens a little the metal by its presence in solid solution while boron and sulfur precipitate at grain boundaries and niobium slows crystallization / growth. This causes a strong slowdown in crystallization, visible on the higher elastic limit, as well as an acceptable increase in magnetic losses.

Example D shows stronger additions of Mn and B while tantalum remains at the same level as in alloy C, and vanadium is lowered to 1%. The performances are always in accordance with the invention. The much higher boron addition results in strong trapping of seeds and grain boundaries, further increasing elastic limits and magnetic losses.

Example E has undergone strong additions of C, Si, Cr and Nb while the percentage of cobalt is reduced to 27%, making it a substantially less magnetically powerful alloy, but also much less expensive. The percentage of vanadium is reduced to a very low level because there is no more ordering weakening for such a percentage of cobalt. The magnetic performances obtained still remain in the target range of property, even if the magnetic losses after additional annealing of magnetic optimization reach a rather high level (81 W / kg) but nevertheless in accordance with the targeted properties (<100 W / kg).

In Example F, part of the vanadium is replaced by tungsten, compared with the reference alloy A. The performances are only slightly changed, and in any case remain in the range of properties sought.

In Example G, part of the vanadium is replaced by zirconium. Zr being a germination inhibitor and grain growth a little less powerful than Nb, we see that the elastic limit values and magnetic losses are increased (relative to alloy A), and in any case in the spectrum of properties referred.

In Example H more than 3% Ni is added which is known to further increase the ductility of the material as well as the electrical resistivity. However saturation magnetization is reduced but still in accordance with the invention, like all other properties characterized.

By way of comparison, similar tests were carried out for alloy compositions not in accordance with the invention.

The chemical compositions of the samples used, as well as the properties obtained, are reported in Table 9. <u> Table 9: Influence of the composition on the mechanical and magnetic properties (2) </ u> Sample I J K The M NOT O P VS 0,008 0.012 0,008 0,013 0,001 0,007 0.0011 0.0016 mn 0.22 0,013 0,028 0.067 0,011 0,019 0,028 0,022 Yes 0.033 0,017 0.13 0,039 3.2 0.03 0,019 0.033 S 0.0028 0.0018 0.0017 0.0031 0.0019 0.0037 0.0022 0.0012 P 0.0027 0.0037 0.0023 0.0025 0.0022 0.0041 0.0038 0.0024 Or 0.1 0.14 0.11 0.16 0.16 0.23 0.18 6.03 Cr 0,025 0,052 3.52 3.8 0.031 0.049 0.016 0,011 MB <0.005 0,025 <0.005 <0.005 <0.005 <0.0050 <0.005 <0.005 Cu 0,018 0,032 0,022 0,018 0.031 0,011 0,017 0.012 Co 15.1 48.64 48,59 48,49 48.67 48.58 48.81 48.71 V <0.005 3.81 <0.005 1.93 <0.005 1.97 1.93 1.98 al <0.005 <0.005 <0.005 <0.005 <0.005 <0.005 <0.005 <0.005 Nb <0.001 <0.001 <0.001 <0.001 <0.001 0.65 <0.001 <0.001 Ti <0.005 <0.005 <0.005 <0.005 <0.005 <0.005 <0.005 <0.005 N2 0.0038 0.0029 0.0031 0.0044 0.0028 0.0024 0.0018 0.0028 Your <0.0008 <0.0008 <0.0008 <0.0008 <0.0008 <0.0008 <0.0008 <0.0008 Zr <0.0008 <0.0008 <0.0008 <0.0008 <0.0008 <0.0008 <0.0008 <0.0008 B <0.0006 <0.0006 <0.0006 <0.0006 <0.0006 <0.0006 0.11 <0.0006 Fe 84.49 47.25 47.585 45.47 47.89 50.41 48.88 43.19 W <0.005 <0.005 <0.005 <0.005 <0.005 <0.005 <0.005 <0.005 Js (T) 2.22 2.29 2.26 2.21 2.23 2.33 2.34 2.23 Hc (A / m) 143 955 255 382 163 446 573 836 Nplis 20 18 1 20 2 20 1 20 Dec. TB B MY TB MY TB MY TB R0.2 (MPa) 485 526 509 four hundred ninety seven 577 620 823 580 Losses (W / kg) (1) 146 442 123 162 88 213 268 395 Losses (W / kg) (2) 127 373 32 25 28 143 77 328 Inv? NO NO NO NO NO NO NO NO

Example I, for which the composition comprises 15% Co, saturates at Js = 2.22T which is below the minimum limit of 2.25T desired. This shows the interest of having at least 18% of Co. Indeed FeCo alloys are sought for their high saturation magnetization which allows them to reduce the masses and volumes of electrotechnical machines in embedded systems (space, aeronautics, railway , automobile, robotics ...).

The composition according to Example J contains 3.8% vanadium, which exceeds the maximum limit of 3% V + W. With such a percentage, one penetrates importantly in the two-phase α + γ domain, which generates a strong degradation of the magnetic performances after additional annealing of optimization of the performances (850 ° C / 3h), placing them well above the desired limit of 100W / kg.

The composition according to Example K contains 3.5% of chromium, but not of vanadium, which enables it to have sufficient saturation magnetization (2.26T) but very poor folding and cutting ability. This is due to the fact that unlike vanadium, chromium does not have the capacity to slow the weakening order of FeCo around 50% Co +/- 25%. The hot-rolled and cold-rolled strips then annealed at the parade are therefore fragile.

Example L bypasses the previous problem by reintroducing 2% of vanadium, as in the reference alloy A, with in addition, and as in the previous example K, a percentage of chromium greater than 3%. The metal becomes ductile and cut after annealing, but the rate of addition of non-magnetic elements is too high and, by dilution of the atomic magnetic moments of iron and cobalt, the saturation magnetization Js becomes lower (2, 21T) to the required lower limit of 2.25T.

The composition according to Example M does not contain vanadium but contains 3.2% of silicon. With such a percentage, the alloy is no longer ductile, because silicon does not slow the weakening order as does vanadium. On the contrary, the silicon hardens the alloy and weakens it by a tendency to order the stoichiometric compound Fe ₃ Si. In addition, a percentage of 3.2% of silicon is pass the saturation magnetization Js below the minimum limit of 2.25T (indeed Si is a non-magnetic element and therefore dilutes the magnetic moments of Fe and Co).

The composition according to Example N contains 2% vanadium, just like the reference alloy A, and also contains 0.65% of niobium, which is greater than the limit of 0.5% according to the invention. Now, niobium is known not only as a potent inhibitor of germination, recrystallization and grain growth, but also as a creator of carbonitrides of Nb and Laves (Fe, Co) ₂ Nb phases, when the percentage of niobium becomes important. These phases and precipitates further slow the migration of the grain boundaries, but especially deteriorate the magnetic properties by effective anchoring of the walls of Bloch. This results in high losses (143W / kg) after additional annealing of magnetic performance optimization.

The composition according to Example O contains 0.11% boron, which is well above the maximum limit of boron according to the invention (0.05%). This causes a very great fragility of the material to the fold and poor cutability: The precipitation of Fe and Co borides is such that the grains are weakened and that the metal has lost any ductility.

Example P explores the important addition of nickel (6.03%) while the composition remains very similar to the reference alloy A: not only the saturation magnetization becomes too weak (2.23 T < 2.25T minimum), but the magnetic losses after additional annealing of magnetic performance optimization (850 ° C-3h) become very high (328 W / kg). Nickel indeed stabilizes the γ phase, and such an alloy causes the strong presence of non-magnetic γ phase in the middle of the ferromagnetic ferrite phase. The material is therefore magnetically soft and the magnetic losses are very important.

The tests of the above tables show that the process according to the invention makes it possible to produce by annealing in the industrial process a thin FeCo strip which can be cut into complex shapes, for example on a press, while allowing elastic limits to be obtained in a very high degree. wide range possible - typically 450 to 1150MPa - without exceeding losses at 2T / 400Hz of 500W / kg (for a thickness of 0.2mm), and preferably less than 400W / kg, while ensuring that very low magnetic losses can be found after a conventional static additional annealing 850 ° C.

• la composition chimique est conforme à l'invention,
• la vitesse de refroidissement du métal en sortie de recuit au défilé et déterminée entre la température de palier et 200°C est d'au moins 600°C/h, et de préférence au moins 1000°C/h
• la température de palier est d'au moins 700 °C, de préférence au moins 720°C,
• la température de palier est d'au plus 900°C.

These properties are obtained if:

• the chemical composition is in accordance with the invention,
• the cooling rate of the metal at the outlet of the annealing outlet and determined between the bearing temperature and 200 ° C. is at least 600 ° C./h, and preferably at least 1000 ° C.
• the bearing temperature is at least 700 ° C, preferably at least 720 ° C,
• the bearing temperature is at most 900 ° C.

Finally, aging tests were carried out at 200 ° C. with holding times of 100 hours and 100 hours + 500 hours cumulative. These tests were carried out at 200 ° C. because this temperature corresponds approximately to the maximum temperature at which materials constituting the yokes of rotating electrotechnical machines used under normal operating conditions can be subjected. For this purpose, tests were made with an alloy of the AFK502R type for two standard grades corresponding to static annealing at 760 ° C. for two hours and 850 ° C. for three hours, and for bands according to the invention corresponding to annealing at run at the temperature of 880 ° C for three scroll speeds: 1.2 m per minute, 2.4 m per minute and 4.8 m per minute in a furnace having a useful length of 1.2 m. During these tests, B 1600 (the magnetic induction for a field of 1600 A / m), the Br / Bm ratio of the magnetic induction remanent at the maximum magnetic induction and the coercive field H _C were measured. The results are reported in Table 10. <u> Table 10: Aging Tests </ u> annealing Aging time at 200 ° C B 1600 (Tesla) Br / Bm Hc (A / m) Static at 760 ° C / 2 h 0 h 2.2070 0.71 97 100 h 2.1700 0.75 102 100 h + 500 h 2.1600 0.75 107 Static at 850 ° C / 3 h 0 h 2.2500 0.62 45 100 h 2.1850 0.68 58 100 h + 500 h 2.2000 0.69 58 Parade 880 ° C v = 1.2 m / min 0 h 1.8200 0.55 83 100 h 1.7700 0.48 88 100 h + 500 h 1.7750 0.49 85 Parade 880 ° C v = 2.4m / min 0 h 1.7650 0.41 96 100 h 1.8250 0.57 75 100 h + 500 h 1.8350 0.59 74 Parade 880 ° C v = 4.8 m / min 0 h 1.6450 0.82 684 100 h 1.6650 0.83 652 100 h + 500 h 1.6600 0.83 644

The results show that, for statically annealed samples, the induction B for a 1600 A / m field decreases by 2% as a result of the annealing, while the coercive field Hc increases by 10% (Heat treatment at 760 ° C. ) or 25% (heat treatment at 850 ° C).

For the annealed samples, the induction B for a field of 1600 A / m, varies by at most 2% following the annealing and the coercive field Hc of at most 23%.

These results show that the annealed annealed alloys are not more sensitive to aging than the annealed annealed alloys. Thus, with an alloy as defined above, that is to say containing from 18 to 55% of Co, from 0 to 3% of V + W, from 0 to 3% of Cr, from 0 to 3% of Si, from 0 to 0.5% of Nb, from 0 to 0.05% of B from 0 to 0.1% of C, from 0 to 0.5% of Ta + Zr, from 0 to 5% of Ni, from 0 to 2% Mn, the rest being iron and impurities resulting from the preparation and in particular an alloy of the AFK502R type, it is possible to manufacture magnetic components and especially magnetic shields, by cutting by mechanical cutting parts in cold rolled strips continuously annealed to obtain the desired mechanical characteristics taking into account the intended application and, according to this application, by performing or not performing on these possibly assembled cut pieces, a complementary annealing of quality intended for optimize the magnetic properties of the alloy.

For each application and each particular alloy, a person skilled in the art knows how to determine the desired mechanical and magnetic characteristics, as well as to determine the particular conditions of the various heat treatments that make it possible to obtain them. Of course, the cold-rolled strips are obtained by cold rolling hot-rolled hyper-tempered strips to maintain a substantially disordered structure. The person skilled in the art knows how to manufacture such hot-rolled strips.

In addition, an oxidation heat treatment can be performed to ensure the electrical isolation of the parts of a stack as is known to those skilled in the art.

Those skilled in the art will understand the interest of this process which allows on the one hand to reduce the number of alloy grades necessary to meet the various needs of users, and on the other hand to very significantly reduce the number of static heat treatments to be performed on the cut pieces.

Moreover, it will be understood by those skilled in the art that the chemical compositions indicated define by a lower bound and an upper bound that the elements to be present. The lower limits of the contents of elements optionally present have been set at 0%, it being understood that these elements may still be present at least in the form of traces, more or less detectable with the known analysis means.

Claims (6)

1. A method for manufacturing a strip in a soft magnetic alloy capable of being mechanically cut out, the chemical composition of which comprises by weight: 18% ≤ Co ≤ 55% 0% ≤ V+W ≤ 3% 0% ≤ Cr ≤ 3% 0% ≤ Si ≤ 3% 0% ≤ Nb ≤ 0.5% 0% ≤ B ≤ 0.05% 0% ≤ C ≤ 0.1% 0% ≤ Zr+Ta ≤ 0.5% 0% ≤ Ni ≤ 5% 0% ≤ Mn ≤ 2% The remainder consisting of iron and impurities resulting from elaboration,
   according to which a strip obtained by hot rolling of a semi-finished product consisting of the alloy is cold-rolled in order to obtain a cold rolled strip with a thickness of less than 0.6mm,
   characterized in that, after cold rolling, a continuous annealing treatment is carried out on the strip by having it pass into a continuous oven, at a temperature comprised between the order/disorder transition temperature of the alloy and the ferritic/austenitic transformation point of the alloy, followed by rapid cooling down to a temperature below 200°C, the cooling rate of the strip upon exiting the continuous oven being greater than 1000°C/h, the cooling rate of the strip between the order/disorder transition temperature of the alloy and 200°C being greater than 1,000°C/h.
2. The method according to claim 1, characterized in that the annealing temperature is comprised between 700°C and 930°C.
3. The method according to claim 1, characterized in that the annealing temperature is comprised between 720°C and 900°C.
4. The method according to any of claims 1 to 3, characterized in that the passing speed of the strip is adapted so that the dwelling time in the continuous oven of the strip at the annealing temperature is less than 10 mins.
5. The method according to any of claims 1 to 4, characterized in that the passing speed of the strip in the continuous oven and the annealing temperature are adapted for adjusting the mechanical strength of the strip.
6. The method according to any of claims 1 to 5, characterized in that the chemical composition of the alloy is such that: 47% ≤ Co ≤ 49.5% 0.5% ≤ V ≤ 2.5% 0% ≤ Ta ≤ 0.5% 0% ≤ Nb ≤ 0.5% 0% ≤ Cr < 0.1% 0% ≤ Si < 0.1% 0% ≤ Ni < 0.1% 0% ≤ Mn < 0.1%